The use of implant devices in the management of many orthopedic conditions is well known in the art. In some cases, the use of such internally-fitted devices may be the only effective way of stabilizing fractured bones. However, this approach suffers from the drawback that, once in place, the length and/or position of the implant cannot be physically manipulated without further surgical intervention. This is a particular drawback when implants are used in order to achieve one or both of the following clinical goals:                a) increase or decrease in bone length, and        b) accelerated healing of bone fractures.        
It is known in orthopedic surgery to sever a bone, such as a tibia or femur, in order to increase its overall length and thereby correct a skeletal or other defect. One common procedure for this purpose makes use of a special nail that is implanted in an intramedullary fashion into the bone to be lengthened. A longitudinally-adjustable frame external to the appendage containing the bone to be lengthened is secured at one end of the bone and it is attached at its other end to the nail as well as to the other end of the bone.
The bone is then osteotomized by the surgeon and the adjustable frame is periodically lengthened, thereby causing the bone, while the break therein is knitting, to assume a desired overall length. The implant is then embedded in the lengthened bone.
As pointed out in U.S. Pat. No. 5,704,938 to Staehlin et al. (1998) the external frame fixation system used in this known bone lengthening procedure is difficult to securely locate on the patient and not only gives rise to discomfort, but it also presents an unattractive appearance. Moreover, pins anchored in the bone and protruding through the skin to join the frame increases the risk of infection and nerve injury, either immediate or delayed, during the lengthening procedure.
To overcome these drawbacks, Staehlin provides a bone-lengthening device which is wholly implantable, except for a tube extending from the device and passing through the skin to supply a hydraulic fluid to the implant which is hydraulically adjustable in length.
Staehlin's two-part implant is mechanically complicated, for it includes a drive bolt located in one part that extends into the other part, which bolt, when rotated by a drive mechanism is activated by a hydraulically-operated plunger making it necessary to supply through a tube leading into the implant a pressurized hydraulic fluid.
In their least complicated forms, bone fractures may be treated by simple immobilization of the relevant body part. In many case, particularly when the fracture occurs in a long bone, this type of management may be sufficient to permit the body's natural processes to completely close the fracture and to lead to complete healing of the affected bone. In other cases, the distance between the mating surfaces of a fractured bone may be so great as to result in non-union of the fracture. Clinically, non-union of fractures is often defined as failure of the fracture fragments to unite after 8 months. Typically, such a situation can arise from excessive movement at the fracture site, soft tissue interposition, infection, or trauma. In such cases, the normal process of calcification fails to take place and the fracture gap remains occupied by fibrocartilage and/or fibrous tissue. Ingrowth of new blood vessels cannot take place, and normal healing will be prevented.
It has been found that application of cyclic compressive forces to the fracture (in imitation of the normal weight bearing forces) accelerates this process by up to one third of the normal healing time. This effect will be discussed in more detail hereinbelow.
Currently, long bone fractures are preferably treated by the use of intramedullary nails or rods. The stability of these implant devices, and the reduced soft tissue damage caused thereby, render this approach preferable over open reduction techniques. However, although these implants permit weight bearing forces to be exerted thereon, they often isolate the fracture from compression forces due to the presence of locking screws, whose primary purpose is to prevent rotation. Also, as a result of the fixed distance between the fracture ends imposed on the fracture by virtue of their rigid structure, intramedullary nails can actually cause cases of fracture of non-union. Various studies have estimated that the incidence of non-unions that result directly from the use of intramedullary nails may reach up to 5% of all fracture cases treated with these devices.
Various other techniques for managing non-union fractures have been used and reported in the art. For example, different forms of electrical stimulation have been investigated. These basic studies have in turn led to a number of proposals for promoting the healing of bone fractures, including invasive treatments involving the use of implanted electrodes as well as non-invasive techniques utilizing electrostatic and electromagnetic fields.
U.S. Pat. No. 3,745,995, for example, describes metal splints that are affixed to fractured bone by means of screws. The device further comprises pickup coils having terminals connected both to said splints and to electrodes invasively inserted into the bone. A coil surrounding the limb having the fracture induces in the pickup coils an alternating current signal. In this way, the electrical signals are transmitted to the fracture ends.
In another approach, the use of mechanical stimuli to promote healing of non-union fractures has been described. For example, in one study [J. Kenwright & A. E. Goodship, Clin. Ortho. & Rel. Res. (1989) 241: 36–47] the effects of mechanical stimulation on midshaft tibial breaks were investigated in experimental animals. The applied stimulation had frequencies approximating that of the walking frequency of the animal used. Cyclic loading of the fracture region for 17 minutes per day was used. Although useful results were obtained in these experimental studies, it was found that it was critical to accurately control the displacements of the fractured bones, as high displacements were noted to lead to mechanical failure of the wound healing process.
U.S. Pat. No. 6,022,349 describes a method and system for treating bone fractures and osteoporosis that is based on the mechanical stimulation described in the aforementioned study by Kenwright and Goodship. However, it would appear that the apparatus described therein is not capable of producing the controlled, axially-directed oscillatory movements that imitate normal force-loading on the affected limb (e.g. the cyclic compression that occurs during walking), that have been shown to be useful in accelerating fracture healing.
U.S. Pat. No. 6,032,677 discloses a method and apparatus for stimulating the healing of medical implants, particularly those used in dental surgery. The apparatus described therein uses an internally-placed permanent magnet and externally applied electromagnetic field to cause oscillation of the implant within a tooth socket or medullary cavity of a fractured bone.
It is a purpose of the present invention to provide a reliable implant device and method for the alteration of bone length.
It is another purpose of the present invention to provide the aforementioned implant device in a form suitable for the management of bone fractures, particularly long bone fractures, and more particularly, cases of non-union of said long bone fractures.
It is a further aim of the present invention to provide a device for managing bone fractures that will act to prevent the occurrence of fracture non-union, by permitting movement of the fractured bone ends towards each other.
Yet a further purpose of the invention is to provide a device and method for managing fractures that will reduce the time required for complete healing.
It is another purpose of the invention to provide a device and method that may be applied during the initial stages of the treatment of bone fractures.
It is a further purpose of the invention to provide a method for managing non-union fractures or for elongating or shortening bones that does not require the complete immobilization of the patient, or the use of uncomfortable and unaesthetic externally-placed devices such as external fixation frames.
It is yet another purpose of the present invention to provide a device for the management of non-union fractures that overcomes the problems and disadvantages of prior art devices.
It is yet another purpose of the present invention to provide a device for elongating or shortening bones that overcomes the problems and disadvantages of prior art devices.
Further objects and advantages of the present invention will become apparent as the description proceeds.